three.js/examples/js/shaders/PixelShader.js

( function () {

	/**
 * Pixelation shader
 */
	const PixelShader = {
		uniforms: {
			'tDiffuse': {
				value: null
			},
			'resolution': {
				value: null
			},
			'pixelSize': {
				value: 1
			}
		},
		vertexShader: `varying highp vec2 vUv;

			void main() {

				vUv = uv;
				gl_Position = projectionMatrix * modelViewMatrix * vec4( position, 1.0 );

		}`,
		fragmentShader: `uniform sampler2D tDiffuse;
		uniform float pixelSize;
		uniform vec2 resolution;

		varying highp vec2 vUv;

		void main(){

			vec2 dxy = pixelSize / resolution;
			vec2 coord = dxy * floor( vUv / dxy );
			gl_FragColor = texture2D(tDiffuse, coord);

		}`
	};

	THREE.PixelShader = PixelShader;

} )();